This invention relates to a gas absorption process and apparatus, particularly for scrubbing acetylene out of a crude gas mixture containing mostly C.sub.2 hydrocarbons.
The invention is especially directed to an improvement in the operation of a plate column, wherein the crude gas mixture is fed into the lower zone of the absorption column; fresh or regenerated absorption agent is fed to the upper zone of the absorption column; loaded absorption agent is drawn off the bottom of the absorption column and is fed to a regeneration stage; a substantially acetylene-free product gas stream is withdrawn from the head of the absorption column, optionally after separation and recycling of a reflux condensate to the absorption column, and wherein a substantially acetylene-free liquid C.sub.2 stream is introduced into the absorption column between the respective feed points for the crude gas mixture and the absorption agent.
In the extraction of ethylene from a thermally cracked cut of hydrocarbons, a crude gas mixture is obtained containing mostly C.sub.2 hydrocarbons (ethylene, acetylene and optionally ethane). Besides the C.sub.2 hydrocarbons, the crude gas mixture may also contain C.sub.3 hydrocarbons and/or methane. Acetylene is generally removed from the crude gas mixture by scrubbing with an absorption agent selective for acetylene. In this connection, EP-B 0 158 280, corresponding to U.S. Pat. No. 4,655,798, teaches a process comprising passing an additional feed of a substantially acetylene-free, liquid, C.sub.2 stream into the absorption column. Despite the introduction of this acetylene-free C.sub.2 stream, foam is formed time and again in the absorption column, and this foam is highly undesirable since it results in downtime and/or the escape of acetylene into the product gas. The formation of both hydrocarbon-rich and hydrocarbon-poor liquid phases, in addition to the vapor phase, are generally responsible for the foam. These two liquid phases are formed when the saturation limit of the absorption agent is exceeded relative to the hydrocarbons present. But foam formation can also occur far below the saturation limit in the absorption column, particularly under unstable operating conditions.